The capsules to which the present method relates are well known and have been in broad use for many years. Such capsules are generally prepared from an edible natural substance such as gelatine or hydroxypropylmethyl cellulose and are telescopically joined so that they have a partial overlap of the cap-side wall with the body-side wall. Generally, such capsules are utilized in the pharmaceutical and food industries to hold edible and pharmaceutically active materials such as medicines, vitamin preparations and other edibles both solid and liquid.
One of the main targets when preparing capsules comprised of a body and cap is to avoid the propensity for leakage of the formulation through the gap between the cap and body of the capsule. In general, leakage can be minimized by product formulation and eliminated by sealing the two capsule parts together by sealing the junction between the cap and body by using a sealing liquid and/or by coating said junction with a layered solid material often termed banding.
While banding is successful against attempts at physical separation of the cap and body of the capsule, it is susceptible to disruption in the same way that the unmodified shell capsule components are.
Therefore, in the respective field of the art various attempts have been made to seal the cap and the body of the capsule directly to each other by means of a so-called “sealing fluid”.
Prior art for capsule-sealing or banding is contained in the following patents:
U.S. Pat. No. 3,071,513 discloses a sealing fluid comprising a dispersion of an air-drying hydrophilic, film-forming polymer in an organic solvent. The application of the sealing fluid is by dipping the capsules.
U.S. Pat. No. 2,924,920 discloses a three-components mixture containing a polyhydric alcohol, a monohydric alcohol and water. This composition is used to seal capsules by a swelling technique. The process is designed to avoid solvent penetrating the overlap between capsule body and cap.
FR-A-2 118 883 discloses the use of a mixture of alcohol and water in an enteric coating process.
EP-A-0 152 517 discloses the use of thermal energy in conjunction with a mixture of alcohol and water to provide a seal between the cap and capsule body, wherein the fluid is positioned by capillary forces between the cap and the capsule body and subsequently heated in situ.
U.S. Pat. No. 4,756,902 discloses a method for sealing a gelatine capsule having a body and a cap comprising the steps of contacting the juncture of the cap and the body edge with a sealing fluid containing an alcohol-water solution maintained at a temperature of from 40 to 100° C. to form a liquid seal and continuous surfaced capsule; and applying a gelatine band to gird the capsule in the area of the liquid seal.
However, all the methods for banding hard capsules by using solutions suffer from several drawbacks. Thus, often capsule shells loose their strength when they are wetted by the water contained in the sealing solution leading to shell deformation, leaking and shell shrinkage at the sealing/banding area.
Hydroxypropylmethyl cellulose capsules are now well accepted as a non-animal alternative to the gelatine capsule. Its use is now very similar to the gelatine capsule; there are needs for tamper resistance as well as to tighten the capsules when filled with liquid formulas.
Furthermore, in general hard capsules using hydroxypropylmethyl cellulose as a base are treated on the external surface during their production with a gliding enhance agent to assure a good functioning performance on the high-speed filling equipment. Due to the presence of this agent, the sealing/banding edge often is irregular.